They camped overnight in the rain, anxious not to miss the chance to say goodbye to their beloved Madiba.

Tens of thousands of mourners were expected to flood into the FNB Stadium in Johannesburg last night (NZ time) to mark the death of Nelson Mandela.

They were being joined for a few hours by one king, 53 presidents and 13 prime ministers, including John Key. Dignitaries have not gathered in such number since the funeral of Pope John Paul II.

Behind bullet-proof screens, President Barack Obama and four of his predecessors were to stand shoulder to shoulder with British Prime Minister David Cameron, Prince Charles, Australian Prime Minister Tony Abbott and UN Secretary-General Ban Ki Moon, as well as celebrities Naomi Campbell, Oprah Winfrey and Annie Lennox.

Strict protocol dictated they would be seated alphabetically by country, to ensure no embarrassing encounters.

Mr Cameron was to be separated from Zimbabwean President Robert Mugabe and Mr Obama from Cuban President Raul Castro and Venezuela's Nicolas Maduro.

Japan and China were also to be kept apart amid simmering tension in the region. One local paper dubbed the arrangements as "eggshell diplomacy".

South African President Jacob Zuma was to deliver the keynote address. General Thanduxolo Mandela was to speak on behalf of the family. Mr Mandela's friend, Andrew Mlangeni, who served time with him in Robben Island prison, was to share his memories. The mood was expected to be a mix of sombre reflection and celebration of the former president's 95 years.

A gloomy day dawned over the calabash-shaped stadium, uncharacteristically cold and wet for the Johannesburg summer. The reddish-brown venue will be familiar to football fans as the venue for the Fifa World Cup final in 2010 - also Mandela's last public appearance.

Umbrellas were banned for security reasons, but the wet weather was not expected to deter mourners. The government laid on free transport and closed many surrounding roads. But there were expected to be chaotic scenes as the crowds massed.

More than 2000 journalists and crew were accredited for the service and events later this week, with some queueing up to eight hours to get their hands on the coveted passes.

Secret service and intelligence agents had earlier prowled the venue and surrounding areas, and a no-fly zone was in place, with fighter jets patrolling the skies as world leaders jetted in.

Also expected to be present for the four-hour service were singer Peter Gabriel and British tycoon Richard Branson, as well as former UN secretary-general Kofi Annan.

Mr Key was joined by Labour leader David Cunliffe but was forced to leave the rest of his five-person delegation back at the hotel after numbers were restricted.

From today, Mr Mandela's body will lie in state at the Union Buildings in Pretoria, ahead of his hometown funeral in Qunu, on Monday.